Cell therapy employs a technique in which cells from a living donor are implanted into a patient either directly or after being cultured in vitro. Cells for use in such treatment are suspended in a solution suitable for the treatment, or adjusted to a suitable concentration prior to implantation. Unfortunately, cells may not be obtained from a living donor at a sufficient cell concentration for treatment. Moreover, in vitro cultures of cells taken from a living donor often contain unnecessary tissue-derived components, culture media, and the like. Accordingly, the following processes are necessary prior to using cells taken from a living donor or cultured cells for treatment: removing unnecessary components and media, suspending (washing) the cells in a solution or other media suitable for the treatment, and concentrating the cells to a level suitable for the treatment.
To achieve this goal, concentration and washing processes using centrifugation have been used. For example, a technique of separating and concentrating regenerative cells from human tissues by centrifugation is disclosed (Patent Literature 1). Unfortunately, such processes using centrifugation can be implemented in a limited number of facilities because of the necessity of a large-scale device, a burden on cells, and increased costs. Another problem is that when the supernatant of a cell suspension obtained after the cells are sedimented by centrifugation is removed for washing, the cells may be exposed to atmospheric air, which may cause contamination, for example.
To solve this problem, it has been proposed to separate and filter a cell suspension using hollow fiber separation membranes, which are compact and simple devices (Patent Literature 2). For use in concentrating a cell suspension for cell therapy, hollow fiber separation membranes with large pore sizes are thought to be suitable because the concentration process should be carried out in a short time to reduce damage to cells and also because unnecessary components and medium components have high molecular weights. Unfortunately, hollow fiber separation membranes with large pore sizes may cause clogging with cells, and the like, or may allow more cells to adhere to the hollow fiber separation membranes, resulting in a reduced number of cells in the process of preparing the concentrate.